Tandem type electrophotographic color laser image forming devices (e.g., printers) are known. Such printers include a plurality of image forming units each of which is specific for one of the plurality of colors (e.g., yellow, magenta, cyan and black) and the image forming units are arranged in tandem (i.e., series). Each of the image forming units is generally made up of a laser scanner and an electrophotographic process device. The laser scanner is typically used to generate, modulate and deflect a laser beam to form an electrostatic latent image on a photosensitive member, and the electrophotographic process device develops the formed electrostatic latent image into a visual image. Each color image developed on the photosensitive member of each image forming unit is sequentially transferred and overlaid one over the other on a sheet of paper in order to form a full-color image.
As the tandem printer generally employs a plurality of image forming units (e.g., four image forming units corresponding to four different colors (e.g., yellow, magenta, cyan and black)), the printer size and the manufacturing cost of such printers tend to be higher than monochromatic printers.
U.S. Pat. No. 5,784,094 discloses a tandem type printer in which a laser scanner is shared among all the image forming units in order to provide a smaller tandem type printer. Specifically, the printer disclosed therein is designed such that four laser beams that are modulated according to image data for each color are directed to one polygon mirror, and the beams deflected by the polygon mirror are led to respective photosensitive members provided in the electrophotographic process device associated with each color.